Prostate cancer (PCa) is the most common type of cancer, excluding skin cancer, and the second leading cause of cancer death in adult men in the USA. Androgen deprivation is currently the only effective therapy for advanced prostate cancer. After an initial regression of the cancer, a majority of patients relapse and develop hormone refractory prostate cancer (HRPC). HRPC cells continue to express androgen receptor (AR), which is functional as evidenced by the expression of androgen-dependent genes such as prostate specific antigen. The long-term objective is to identify the mechanisms involved in the ligand-independent activation of the AR in HRPC cells. PCa metastasizes to the bone where it forms osteoblastic lesions, and studies suggest that bone morphogenetic proteins (BMPs) may be involved in this process. The function of BMP signaling in normal and PCa remains to be elucidated. BMPs are members of the TGF-beta superfamily of growth factors. BMPs signal through cell-surface receptors via Smad signal transduction proteins. Upon ligand activation, Smads are translocated from the cytoplasm to the nucleus where they bind DNA and modulate transcription. Smads can form complex with and activate steroid receptors such as Vitamin D receptor. Preliminary data suggest that Smad-5 is up-regulated in HRPC cells. In this study, it is hypothesized that the increase of Smad 5 expression in HRPC cells allows for the formation of a Smad-5/AR complex, which modulates AR transactivation in an androgen-independent manner. To test this hypothesis the following specific aims are proposed: Specific Aim 1: To test the hypothesis that Smad-5 expression is up-regulated in the progression from androgen-sensitive PCa to HRPC in cell lines and tumors. a) Determine the expression profiles of Smad-5 mRNA. b) Determine the expression and localization of Smad-5 protein. Specific Aim 2: To test the hypothesis that Smad-5 forms a complex with the AR which can regulate androgen responsive gene expression. a) Determine the ability of Smad-5 to form a complex with AR. b) Determine the functional capabilities of the Smad-5/AR complex. Specific Aim 3: To test the hypothesis that Smad-5 over expression is regulated by BMP signaling. a) Characterize BMP-4, -7 & -8 mRNA and protein expression in androgen-sensitive and HRPC cell lines and a cohort of tumors representing androgen-sensitive and androgen refractory PCa. b) Characterize Smad-5 expression after treatment with BMPs.